@phdthesis{Scharf2011,
  author    = {Sandra Scharf},
  title     = {Characterizing the Interaction of the Pathogen Staphylococcus aureus with its Human Host by Transcriptomic and Proteomic Approaches},
  journal    = {Transkriptom- und Proteomanalytische Studien zur Interaktion des pathogenen Erregers Staphylococcus aureus mit seinem menschlichen Wirt},
  url       = {https://nbn-resolving.org/urn:nbn:de:gbv:9-000899-7},
  year      = {2011},
  abstract  = {Staphylococcus aureus is a commensal colonizing 20-30\% of the population as well as a pathogen causing diverse diseases ranging from skin infections via toxin mediated diseases to life threatening conditions. In its interplay with the human host, this microorganism resorts to an extensive repertoire of both membrane-bound and secreted virulence factors facilitating adhesion to, invasion of, and spreading into various host tissues. Among the numerous virulence factors produced by S. aureus are the staphylococcal superantigens (SAgs). They directly cross-link conserved regions of the T cell-receptor with MHC class II molecules (outside the peptide-binding cleft) on antigen presenting cells. This results in a strong stimulation of up to 20\% of all T cells which respond with proliferation and massive cytokine release. Recently, the enterotoxin gene cluster (egc) located on a pathogenicity island was described. The egc-genes are the most prevalent SAg genes in commensal and invasive S. aureus isolates. However, they appear to cause toxic shock only very rarely and their presence is negatively correlated with severity of S. aureus sepsis. Therefore it was suggested that SAgs might differ in their pro-inflammatory potential. In addition to their superantigenicity, SAgs also act as conventional antigens and induce a specific antibody response. In contrast to non-egc SAgs, despite the high prevalence of egc SAgs, neutralizing antibodies against egc SAgs are very rare, even among carriers of egc-positive S. aureus strains. In order to find an explanation for this “egc-gap”, we have tested two non-exclusive hypotheses: (i) egc and non-egc SAgs have unique intrinsic properties and drive the immune response into different directions and (ii) egc and non-egc SAgs are released by S. aureus under different conditions, which shape the immune response to them. To test these hypotheses, we compared the effects of egc and non-egc SAgs on human blood cells. Their T cell-mitogenic potencies, the elicited cytokine profiles as well as their impact on gene expression were highly similar. Both egc and non-egc SAgs induced a very strong pro-inflammatory response. In contrast, the regulation of SAg release by S. aureus differed markedly between egc and non-egc SAgs. Egc-encoded proteins were secreted by S. aureus during exponential growth, while non-egc SAgs were released in the stationary phase. We conclude that the distinct biological behavior of egc and non-egc SAgs is not due to their intrinsic properties, which are very similar, but is caused by their differential release by S. aureus. Traditionally, S. aureus has not been considered as an intracellular pathogen but strong evidence emerged indicating that staphylococci can invade and persist in various cell types. Internalization might constitute a bacterial strategy to evade the host’s defense reactions and the action of antibiotics. The intracellular niche might thus constitute a reservoir for chronic or relapsing infections. Contrary to their potential importance, genome-wide functional genomics analyses of the adaptation reactions of S. aureus to the host cell environment are rare and so far confined to gene expression profiling. Investigations addressing the proteome of internalized S. aureus are still lacking due to the challenge of obtaining a sufficient number of infecting bacteria. The proteome of other pathogens such as Francisella tularensis has been characterized by classical 2-DE approaches. However, the number of bacteria required for such a 2-DE based approach is often exceeding the numbers available from in vivo infection models. Furthermore, this approach does not allow monitoring of time-dependent quantitative changes in protein levels. Here, a workflow allowing time-resolved analysis of internalized S. aureus by combining pulse-chase stable isotope labeling by amino acids in cell culture with high capacity cell sorting, on-membrane digestion, and high-sensitivity mass spectrometry is presented. This workflow permits detection and quantitative monitoring of several hundred staphylococcal proteins from as little as a few million internalized S. aureus cells. This approach has been used to reveal time-resolved changes in levels of proteins in S. aureus RN1HG upon internalization by human bronchial epithelial cells. Proteins involved in stress adaptation as well as protein folding and some components of the phosphotransferase system were upregulated in internalized staphylococci, whereas proteins of the purine biosynthesis pathway and tRNA aminoacylation were downregulated. Furthermore, regulatory adaptive responses of internalized S. aureus to the intracellular milieu were shown as global regulators displayed increased protein abundance levels compared to non-internalized bacteria. Taken together, we observed changes in levels of proteins with functions in protection against oxidative damage and adaptation of cell wall synthesis in internalized S. aureus.},
  language  = {en}
}